This invention relates to a polyisocyanate composition having excellent storage stability at lower temperature.
Polyisocyanates such as polymethylene polyphenyl poly-isocyanate ("Polymeric MDI" or "C-MDI") are widely utilized as automotive interior parts like steering wheel and instrument pad, daily necessities like adhesive, heat insulators for electric refrigerator, and other structural heat insulators like outer wall panel, pipe and tank in various fields.
Polymeric MDI and its derivatives are widely utilized in the production of a great deal of polyurethane products. Accordingly, the range for storage conditions of those materials has to be broad in actual uses. However, there is few cases in which the storage conditions at a oil drum or can are strictly controlled. Especially, the storage temperature is not usually controlled in a spot foaming like spray foaming construction. Therefore, in winter time, the material storage temperature often reaches to about -10.degree. C. even in everywhere except severe cold regions. On the other hand, research and development activities for improving storage stability of polymeric MDI containing diphenylmethane diisocyanate "MDI" of more than 40 wt % and its derivatives are being continued. As the results, some polymeric MDI, having viscosity of about 170 cps at 25.degree. C., which have excellent storage stability showing that there is no crystallization even at -10.degree. C., are sold on the market by some isocyanate makers.
However, polymeric MDI, having lower viscosity of less than 160 cps, especially, 55 to 140 cps at 25.degree. C., often contains a large amount of MDI having melting point of 38.degree. C. As the result, there is a problem in storage stability that MDI separates from the polymeric MDI at low temperature like about -10.degree. C.
On the other hand, since the from regulation began in 1990 year, the demand for polymeric MDI having lower viscosity and excellent storage stability at low temperature has been increasing. Foaming makers often give severe requirements to isocyanate makers, regarding polyisocyanates having only good storage stability at low temperature. However, it has never been known until now about additives which are soluble in polymeric MDI which gives the smallest changes of its reactivity and characteristics of resulting polyurethane resins without reducing a large number of isocyanate content "NCO %".
Polymeric MDI usually contains a small amount of insoluble dimer prepared by the bonding between NCO groups. The dimer content in polymeric MDI delicately affects its storage stability at low temperature. Since such dimer is easy to be formed at higher temperature, it is necessary to pay the closest attention to storing these polymeric MDI, and it is eagerly expected that a polyisocyanate having excellent storage stability at lower temperature is developed.